Various physiological, pharmacological, and biochemical data gathered over the past twenty-five years have led investigators to suggest a relationship of catecholamines to human hypertension. The Catecholamine Laboratory of the Mount Sinai School of Medicine has developed biochemical techniques by which human catecholamine metabolism can be evaluated with considerable specificity and sensitivity. Application of the procedures has led to the observation that defective catecholamine metabolism is not only aasociated to a gross degree with tumors of the neural crest but, in a much more subtle manner, with essential hypertension as well. This project is designed to investigate in greater depth, the original observations and their detailed causes, the effects upon catecholamine metabolism caused by drugs known to be of value in the treatment of essential hypertension, and an evaluation of the degree of reliability of certain catecholamine measurements in the differential diagnosis of the manifold types of human hypertension. Isotopically-labeled catecholamines will be administered to human subjects with hypertension as well as various hypertensive animal models in order to further delineate the nature of this defect in norepinephrine metabolism. Blood platelet and erythrocyte uptake mechanisms will be evaluated in hypertensive states and during administration of drugs which modify the function of the autonomic nervous system.